Currently, when it is necessary to completely remove a disc from between adjacent vertebrae, the conventional procedure is to fuse the adjacent vertebrae together. This “spinal fusion” procedure is a widely accepted surgical treatment for symptomatic lumbar degenerative disc disease. However, reported clinical results vary considerably, and complication rates are considered by some to be unacceptably high.
More recently, there have been important developments in the field of disc replacement, namely disc arthoplasty, which involves the insertion of an artificial intervertebral disc implant into the intervertebral space between adjacent vertebrae, and which allows limited universal movement of the adjacent vertebrae with respect to each other.
The aim of total disc replacement is to remove pain generation (disc), restore anatomy (disc height), and maintain mobility in the functional spinal unit so that the spine remains in an adapted sagittal balance. Sagittal balance is be defined as the equilibrium of the trunk with the legs and pelvis to maintain harmonious sagittal curves. In contrast with fusion techniques, total disc replacement preserves mobility in the motion segment and mimics physiologic conditions.
One such intervertebral implant includes an upper part, or upper plate, That can communicate with a vertebrae, a lower part, or lower plate that can Communicate with the adjacent vertebrae, and a pivot element, or third part, inserted between these two parts. An example of an instrument for this type of implant is disclosed in U.S. Pat. No. 5,314,477. More specifically, tongs are disclosed that can be used, after the insertion of the pivot element between the upper and lower parts of the implant, to move the two vertebrae apart to a distance sufficient for introducing the assembled implant into that space. Additionally, instruments exist for inserting intervertebral implants that move the implant along a longitudinal guide as far as the implant point, and then feed the implant out of the guide and into the intervertebral space. See U.S. Pat. No. 5,571,109. However, both of these instruments are suitable only for inserting complete implants.
An improved instrument is shown in Published Application No. WO 01/01893, published Jan. 11, 2001 and incorporated by reference, and instruments for inserting same are shown in Published Application No. WO 01/19295, published Mar. 22, 2001 and incorporated herein by reference. These applications disclose an arrangement wherein the upper and lower parts of the implant, without the pivot element, are inserted into the intervertebral space, after which the upper and lower parts are separated and the pivot element is inserted therebetween. The terms “separated” and “distracted” are used interchangeably and have the same meaning herein.
In particular, the instrument shown in Published Application No. WO 01/19295 includes: a) an upper arm for engaging an upper part of the implant, b) a lower arm for engaging a lower part of the implant, c) a separate distractor for separating the upper and lower parts from each other after they have been inserted into the intervertebral space, and d) a pusher element for pushing the pivot element along the length of the instrument between the two lower arms and directly into the lower part. After location of the pivot element, the distractor is retracted, allowing the two adjacent vertebrae to come together which urges the upper and lower parts together against the pivot element.
While these and other known instruments and methods represent improvements in the art of artificial intervertebral implant insertion, there exists a continuing need in the art for improvements in the field of instruments and methods for inserting intervertebral implants.